The present invention relates to a method for fabricating an electronic device, and more specifically, to a method for removing a reaction product deposited on walls or other portions of a pattern formed by dry etching a processed film such as a conductor film or an insulator film.
In the fabrication of electronic devices, a dry etching technique is often used to form a via hole in an insulator film or to form a conductor film into a wiring pattern. It is known that etching gas, photoresist or a processed film causes a reaction product (a sidewall protective film or a polymer residue) to be deposited on walls of the via hole or the wiring pattern. The deposition of the reaction product on the bottom surface of the via hole formed in the insulator film would cause junction failure, an increase in the resistance of the via contact or corrosion of the wiring pattern (underlying wiring), thereby seriously damaging the reliability of the electronic device.
In order to remove the reaction product, there is a cleaning solution (hereinafter referred to as the conventional cleaning solution) which comprises an aqueous solution of an organic solvent and a fluorine compound having power to etch the insulator film (Refer to Japanese Laid-Open Patent Application Nos. 7-201794 and 10-55993).
In recent years, as electronic devices are highly micromachined, new resist materials have been introduced to increase the etch selectivity, and new etching gases (C5F8 and the like) with a small global warming coefficient have been introduced to show consideration for environmental problems. As a result, a reaction product having different components from conventional ones is caused in higher volume, making it difficult to remove the reaction product by using the conventional cleaning solution.
In view of the above-mentioned problems, the object of the present invention is to secure the removal of the reaction product deposited on walls or other portions of an etched pattern.
In order to meet the object, the inventors of the present invention have studied the relationship between the amount of a fluorine compound contained in a cleaning solution and the solution""s capability of removing the reaction product.
The method for fabricating the electronic device of a first comparative example will be described as follows with reference to FIGS. 3(a) to 3(c) by taking as an example the case where a via hole is formed by dry etching an insulator film on a wiring and then the reaction product deposited on walls or other portions of the via hole is removed by using a cleaning solution having a relatively low content of a fluorine compound, or having relatively low power to etch the insulator film.
As shown in FIG. 3(a), an underlying wiring 4 having a multi-layer structure consisting of a first titanium nitride film 2A, an aluminum alloy film 3 and a second titanium nitride film 2B was formed onto a substrate 1. After this, an insulator film 5 was formed on the underlying wiring 4, and then a resist pattern 6 having an opening portion in the via hole formation region was formed on the insulator film 5.
Later, the insulator film 5 and the second titanium nitride 2B were sequentially dry etched with the resist pattern 6 as a mask so as to form a via hole 7 as shown in FIG. 3(b), which was followed by the removal of the resist pattern 6 through plasma ashing. At this moment, a reaction product 8 was deposited on walls and the bottom surface of the via hole 7.
The inside of the via hole 7 was washed with the cleaning solution having a relatively low content of a fluorine compound such as ELM-C30-A01 (hereinafter referred to as the cleaning solution A) manufactured by Mitsubishi Gas Chemical Co., Ltd. for 10 to 20 minutes at room temperature (23xc2x0 C.), and then rinsed with water. Later, the substrate 1 was dried.
Consequently, as shown in FIG. 3(c), the portion of the reaction product 8 that had been deposited on the bottom surface of the via hole 7 remained unremoved. In a later process, when a conductor film was buried into the via hole 7 to form a via contact, and an overlying wiring was formed in such a manner as to be connected with the underlying wiring 4 via the via contact, the overlying wiring and the underlying wiring 4 had a junction failure. For this reason, the resistance value of the via contact could not be measured.
Thus, when the cleaning solution has a relatively low content of a fluorine compound, the solution""s capability of removing the reaction product greatly relies on the ability of the organic solvent contained in the cleaning solution to dissolve the reaction product. Therefore, not only it takes more time to remove the reaction product, but also it becomes difficult to remove the product entirely.
The method for fabricating the electronic device of a second comparative example will be described as follows with reference to FIGS. 4(a) to 4(c) by taking as an example the case where a via hole is formed by dry etching an insulator film on a wiring and then the reaction product deposited on walls or other portions of the via hole is removed by using a cleaning solution having a relatively high content of a fluorine compound, or having relatively high power to etch the insulator film. The processes shown in FIGS. 4(a) and 4(b) in the second comparative example will not be explained because they are the same as the processes shown in FIGS. 3(a) and 3(b) in the first comparative example.
In the second comparative example, the inside of the via hole 7 was washed with a cleaning solution having a relatively high content of a fluorine compound such as ELM-C30-A10 (hereinafter referred to as the cleaning solution B) manufactured by Mitsubishi Gas Chemical Co., Ltd. for 10 to 20 minutes at room temperature (23xc2x0 C.), and then rinsed with water. After this, the substrate 1 was dried. The cleaning solution B contains about 8 times as much fluorine compound, and has 50 to 200 times as high power to etch an insulator film as the cleaning solution A. The etching power can be the amount of etching the same type of insulator film in the same duration in time.
As a result, as shown in FIG. 4(c), while the reaction product 8 was entirely removed, the portion of the insulator film 5 that was in the vicinity of the via hole 7 was also removed at the same time. In FIG. 4(c) the broken line indicates the positions of the walls and bottom surface of the via hole 7 formed at predetermined dimensions.
If the inside of the via hole 7 washed with the cleaning solution B is then rinsed with water, the cleaning solution B diluted with the water will become capable of corroding the conductor film contained in the underlying wiring 4, namely, the aluminum alloy film 3. To be more specific, the ability of the cleaning solution B to corrode the aluminum alloy film 3 during the rinse with water, that is, the cleaning solution B""s capability of corroding the aluminum alloy film 3 in the rinse water is about 3 times as high as the cleaning solution A""s capability (the maximum value) of corroding the aluminum alloy film 3 in the rinse water.
FIG. 5(a) is a schematic view of the strengths of streams of water inside the via hole 7 while it is being rinsed with water according to the method for fabricating the electronic device of the second comparative example. The arrows xe2x80x9caxe2x80x9d to xe2x80x9cexe2x80x9d represent streams of water at the respective portions inside the via hole 7, and their lengths correspond to the strengths of the streams of water.
FIG. 5(b) shows changes in the concentration of the cleaning solution B inside the via hole 7 while it is being rinsed with water according to the method for fabricating the electronic device of the second comparative example. The changes in the concentration of the cleaning solution B are shown in correspondence with the streams of water indicated by the arrows xe2x80x9caxe2x80x9d to xe2x80x9cexe2x80x9d of FIG. 5(a).
As shown in FIG. 5(a), the streams of water become less and less powerful as they are closer to the bottom surface of the via hole 7. The reason for this is considered that the strengths of the streams of water inside the via hole 7 depend on the rate of dispersion of the water stream at the top of the via hole 7. As shown in FIG. 5(b) the closer to the bottom surface of the via hole 7, the less the concentration of the cleaning solution B decreases, which causes the portion of the aluminum alloy film 3 that is exposed to the via hole 7 to be in contact with the cleaning solution B for a long time. As a result, in addition to the remaining portion of the reaction product 8 being removed, the exposed portion of the aluminum alloy film 3 is corroded and dissolved to form a hollow portion 9 beneath the insulator film 5 as shown in FIG. 4(c). This results in the formation of a hydroxide in the vicinity of the hollow portion 9 in the aluminum alloy film 3. The via contact formed by burying a conductive film into the via hole 7 was subjected to an acceleration test, and more specifically, a high-temperature storage resistance increase rate test conducted for 1000 hours at a high temperature of 200xc2x0 C. to find that the rate of increase in the resistance value of the via contact (hereinafter referred to as the rate of increase in the via resistance) was over 10%.
The results of the test indicate that a cleaning solution with a relatively high content of a fluorine compound makes the insulator film which underlies the reaction product be etched so as to make it easy to remove the reaction product; however, at the same time, the cleaning solution causes the via hole formed in the insulator film to grow in size and the portion of the conductor film contained in the underlying wiring which is exposed to the via hole to be corroded.
The present invention has been contrived based on the above-mentioned findings. To be more specific, the first method for fabricating the electronic device of the present invention comprises: a first process of forming an insulator film onto a conductive pattern formed on a substrate; a second process of forming an opening portion in said insulator film by dry etching said insulator film using a resist pattern as a mask; a third process of removing a reaction product deposited on a wall or a bottom surface of said opening portion; and a fourth process of rinsing an inside of said opening portion rid of said reaction product with water, the third process including a process of removing said reaction product by using a first cleaning solution having relatively low power to etch said insulator film and a second cleaning solution having relatively high power to etch said insulator film in that order.
In the first method for fabricating the electronic device, the reaction product deposited on walls or the bottom surface of the opening portion formed in the insulator film is removed by using the first cleaning solution with relatively low power to etch the insulator film and the second cleaning solution with relatively high power to etch the insulator film in that order. In this case, the reaction product can be partly removed by the first cleaning solution, and then the remaining part of it can be removed by the second cleaning solution. This can shorten the time to use the second cleaning solution, compared with the case where the reaction product is removed by the second cleaning solution only, which reduces the amount of etching the insulator film. This secures the removal of the reaction product without increasing the opening portion in size.
In the first method of fabricating the electronic device, it is preferable that the first cleaning solution and the second cleaning solution contain the same organic solvent.
In this case, it becomes unnecessary to provide each cleaning solution with an individual drain line, which realizes the centralization of the drain lines.
In the first method of fabricating the electronic device, it is preferable that the first cleaning solution and the second cleaning solution are used in the same cleaning chamber.
In this case, the time required for the removal of the reaction product can be reduced.
The first method of fabricating the electronic device preferably further comprises, between the third process and the fourth process, another process for washing the inside of said opening portion rid of said reaction product by using a third cleaning solution having a lower capability of corroding said conductor pattern in the fourth process than the second cleaning solution.
In this case, after the removal of the reaction product by the second cleaning solution and before the inside of the opening portion is rinsed with water, the second cleaning solution remaining inside the opening portion is replaced by the third cleaning solution. Consequently, the amount of corroding the conductor pattern during the rinse with water can be less than in the case where the inside of the opening portion is rinsed with water immediately after the second cleaning solution is used, which can decrease the size of the hollow portion formed beneath the insulator film.
When the third cleaning solution is used, the third cleaning solution preferably has relatively low power to etch said insulator film.
In this case, the amount of etching the insulator film can be reduced, so that the opening portion can be prevented from increasing in size.
When the third cleaning solution is used, the third cleaning solution is preferably the same as the first cleaning solution.
In this case, the number of types of the cleaning solutions used in the cleaning process can be reduced.
When the third cleaning solution is used, it is preferable that the third cleaning solution substantially has no power to etch said insulator film and substantially has no capability of corroding said conductive pattern in the fourth process.
In this case, it can be secured to prevent the conductor pattern from being corroded during the rinse with water, while the opening portion is prevented from increasing in size.
The second method for fabricating the electronic device of the present invention comprises: a first process for forming a processed film on an underlying film formed on a substrate; a second process for forming an etched pattern by dry etching said processed film using a mask pattern; a third process for removing a reaction product deposited on a wall of said etched pattern; and a fourth process for rinsing said etched pattern or a vicinity thereof rid of said reaction product with water, the third process containing a process for removing said reaction product by using a first cleaning solution having relatively low power to etch said processed film and a second cleaning solution having relatively high power to etch said processed film in that order.
In the second method for fabricating the electronic device, the reaction product deposited on walls of the etched pattern is removed by using the first cleaning solution with relatively low power to etch the processed film and the second cleaning solution with relatively high power to etch the processed film in that order. In this case, the reaction product can be partly removed by the first cleaning solution, and then the remaining part of it can be removed by the second cleaning solution. This can shorten the time to use the second cleaning solution, compared with the case where the reaction product is removed by the second cleaning solution only, which reduces the amount of etching the processed film. This secures the removal of the reaction product without changing the size of the etched pattern.
In the second method of fabricating the electronic device, the first cleaning solution and the second cleaning solution preferably contain the same organic solvent.
In this case, it becomes unnecessary to provide each cleaning solution with an individual drain line, which realizes the centralization of the drain lines.
In the second method of fabricating the electronic device, the first cleaning solution and the second cleaning solution are preferably used in the same cleaning chamber.
In this case, the time required for the removal of the reaction product can be reduced.
The second method of fabricating the electronic device preferably further comprises, between the third process and the fourth process, another process for washing said etched pattern or said vicinity thereof rid of said reaction product by using a third cleaning solution having a lower capability of corroding said underlying film in the fourth process than the second cleaning solution.
In this case, after the removal of the reaction product by the second cleaning solution and before the etched pattern or its vicinity are rinsed with water, the second cleaning solution remaining on the etched pattern or its vicinity is replaced by the third cleaning solution. Consequently, the amount of corroding the underlying film during the rinse with water can be less than in the case where the etched pattern or its vicinity is rinsed with water immediately after the second cleaning solution is used.
When the third cleaning solution is used, the third cleaning solution preferably has relatively low power to etch said processed film.
In this case, the amount of etching the processed film can be reduced, so that the etched pattern can be prevented from changing in size.
When the third cleaning solution is used, the third cleaning solution is preferably the same as the first cleaning solution.
In this case, the number of types of the cleaning solutions used in the cleaning process can be reduced.
When the third cleaning solution is used, it is preferable that the third cleaning solution substantially has no power to etch said processed film and substantially has no capability of corroding said underlying film in the fourth process.
In this case, it can be secured to prevent the underlying film from being corroded during the rinse with water, while the etched pattern is prevented from changing in size.